Quite a few are of course already in the libary. Glass for example. But as told, a few standard things are simply missing. And the addon needs imho a better categorizing and naming of the materials too.

Procedural doesn't make sense where you need real textures. But we will see. First let's make the list. Then let's have a look what exists in the library already. And then let's have a look to fill the gaps. And to throw out what is not needed.

We can of course also have a look if we can update the existing materials to Principled where possible and useful.

EDIT, i would of course love to include as much materials as possible. But a single useful wood texture can easily eat up 50 mb and more. So that's most probably most of the textures out. I don't want to blow up the Bforartists download to a few gigabytes

The download size is of course something to keep an eye on. Despite not having to uv unwrap the objects, keeping it mostly procedual textures also make sense for that. - If the library grows too big, it could always be an additional download for an extended library of course.

What should be included in the BfA download could be "the ESSENTIAL library" (which is also a great name for it.^^) - Maybe it is enough to just include some placeholder textures, if it is treated more like a toolkit of presets, that the user plug in their their own textures. - In that regard one wood material (in some variations, like glossy, matte, raw) would be enough, the rest relys on the creativity of the artist to fill in the textures as needed.

Edit: The "ESSENTIAL" and the "EXTENDED" library could be good names for these features.

Okay, let's make nails with heads, and collect what already exists versus what we want to add.

Current main categories in the addon:

Blender Internal,
Cycles Templates
Cycles Materials
V_Ray

Blender Internal will vanish with 2.8, so we shouldn't even bother to change anything here. V-Ray. Well, it comes with the official Blender version. But V-Ray does not come with Bforartists nor Blender. So no point to keep this materials. That's already two categories that we could remove from the addon.

I have yet to find out the difference between Cycles Templates and Cycles Materials. The templates are in the end materials too. So i would vote to make the Templates a sub category of the Cycles Materials.

That way we have just sub categories for Cycles. Ledt's keep Blender Internal as long as we have the 2.7x line, and we have shrinked the main categories from 4 to 2.

You mentioned essentials and extended. So that could split the Cycles materials into two big categories again.

Anyways. We can do this at a later point. First let's sort the existing Cycles sub categories. That's the first thing that we need to fix i guess. Proper material categories. I made a few comments already.

Templates - the main category that we want to be a sub category. Should contain more complicated templates. See Essential category below.
Car Paint - Should not be a main category. Where could this fit?
Organic - This one could include stuff like skin, fur and leaf shaders
Glass
Textile - Rename to Fabric and leather
Groups - A single entry with Node groups. This one is a template
Utils - Two entries.This one is a template
Metal
Lights
Ceramic
Plastic
Earth - Could become procedural. Or go into the marble category below.
Wood
All

The categories that we want to add here is so far this:

Essential - Simple templates with Texture, Normalmap, etc. . The kind of stuff that you usually start with when you make your own setup, and where you again and again spend a dozen clicks at.

Bricks - maybe this one could be part of the wall main group. We don't need more than two or three bricks examples.
Wall
Rock
Liquids - Water, orange juice, etc.
Marble
Paint
Paper
Ground

"You mentioned essentials and extended. So that could split the Cycles materials into two big categories again."

The essential and extended library would only be a solution to keep the download size small. It should be just one library, with different material categories as written above. - Let's just start making some materials and see how large the download turns out.

I have run into a little problem meanwhile. Adding materials does not work as thought. The add button is broken. Seems that we need to manipulate the existing blend files directly. I just have no idea how to deal with the categories yet. Still investigating.

Okay, i got told how it works to add a material. First be in the main category. Filter must be off. Then create a material. Save the blend file. Add the currently selected material with the Add button. The material should be in the list now. Select it. Choose the category where you want it to be. Then press the "Add, Remove. Reload Apply ..." button. The one with the back arrow icon. And finally tick the filter button. The material should be in the category now. And is stored in the library.

If anyone wants to join creating those materials, please pick a complete category from the list above and create all the related materials for it. - This will be a great exercise. - Just mention which category you will be working on here, so we don´t do double work. - Corrections and improvements can be done later. Let´s first focus on creating all of the materials right now.

If you want to use it, I created a sample scene using the BfA logo as a material placeholder. Download below.

There are of course already the standard materials from the Materials Library VX addon. And we could borrow a few materials from the other addon.

I am currently busy with preparing the next Bforartists version. Which is hopefully done in the next days. Then i'll join this task again, and will have a look to create the new categories and join the first new created materials :)

I just checked out how to put all the materials into the library and it is actually much simpler than that. - All that has to be done is copy the .blend files into the library folder and all of the materials in the scene will show up in the material library. The name of the .blend file becomes the category name.

So all that will have to be done in the end is to clean out all unnessecary materials of the scenes and copy them.:D ... We will have to see if we even keep the blender internal and other materials in there? - I would just go with a clean library, showing only the different material categories.

Can you have a look if it is possible to alter the addon in a way, that the preview is automatically updated when the user clicks on one of the materials? - Right now the addon requires to always click the preview button, which is quite annoying. - An auto update would at least be a step in the direction of faster visual browsing the library here.

Also some bigger and more understandable icons on the sidebar of the addon would help usability.

EDIT: Would it be possible to call the material preview from BfA into the list of the addon? That way a dynamic list with previews could be generated. - Or else, would it be possible to include images in the list? Then we could prerender all of the materials to include a preview that way.

Mh, yes, that's one way of doing it. But i wanted to avoid to have single library files, since it clutters the workflow when you have to reload libs all the time. On the other hand ... in the end i'm open to anything. But then we would need to grab the materials from the existing library, and put them into single files too. So that it is consistent.

I already had a look if we could implement a preview. Two things: we don't maintain addons. And i was simply not able to manage it, sorry.

Yes, that will also be easiest to browse, there is a bit of lag when switching category, but it gives much more overview than having it all in one enormous list.

I gave dynamat a try again and this is really perfect. - It looks like blendermada also uses this. So I contacted the developer to see if we maybe can include it into BfA. - But no answer yet unfortunately.

Hmmm. The biggest problem for the materials library vx addon seems to be the preview, right? We could display the preview window directly in the addon. That's of course a double menu entry then. But for a good reason.

The only thing that would be missing is auto preview then when switching the categories. You would still have to click the preview button. But that's better than nothing i would say